And on the beginning of your months, you shall offer up a burnt offering to the Lord… (Bamidbar 28:11)
The laws of the reading of the Torah state that each aliyah (lit. ascent, call up to recite the blessings over the Torah reading) must contain a minimum number of three verses (Megillah 21b).
Furthermore, the Talmud highlights the fact that the text of the Torah contains spaces between verses which act as paragraph breaks splitting up similar conceptual components of the narrative. The Talmud rules that an aliyah must not begin or end less than three verses from one of these paragraph breaks. The concern is that if someone arrives late or leaves shul at the critical moment, they may suspect that the preceding or following aliyah contained fewer than three verses.
The Torah reading for Rosh Chodesh therefore presents a halachic challenge. The portion for Rosh Chodesh is taken from the first fifteen verses of chapter 28 of Bamidbar. However, the portion has to be split up between four aliyot (plural of aliyah). Due to the paragraph breaks in the text, it is impossible to divide the aliyot without violating one of the principles brought down earlier.
The Talmud seems to conclude that the only resolution is to repeat one of the verses and Rabbeinu Nissim (d. 1376) explains that for the second aliyah weshould repeat the third verse. Yet Nachmanidies (Ramban, d. 1270) points out that repeating the third verse still means that someone who walks in may think that the first aliyah was only two verses long.
The Vilna Gaon (Gra, d. 1797) devised an elegant solution which involves continuing the second aliyah (levi) from verses four through eight and then repeating verses six to eight for the third aliyah before continuing to verse ten. The final aliyah continues from eleven to fifteen. While our tradition follows Rabbeinu Nissim, many communities in Israel follow the opinion of the Gra.
It is fascinating that our traditions go to such lengths to avoid any suspicion of wrongdoing, even from someone who was not in shul for the whole Torah reading.